Imidazoles are curing agents that are receiving attention for providing exceptional curing properties to resin compositions, resulting in cured materials with high heat resistance. However, because of problems with storage stability, extending working life by controlling basicity is being investigated through formation of metal complexes and various types of acid salts. The inventors have filed patent applications (Japanese Patent Application Publication Nos. 9-12683 and 2000-297094) in which a mixture of the general formulas (1), (2), and (3) below or an imidazole group-containing silane coupling agent expressed by the general formula (4) would provide, as curing agents for epoxy resins, curable epoxy resin compositions having exceptional adhesion properties. However, these imidazole group-containing silane coupling agents are disadvantageous in having poor storage stability in the same manner as do conventional imidazoles.
Poor storage stability when mixed with epoxy resin is also a problem with silane coupling agents such as amino group-containing silane coupling agents (commercial products), dialkylamino group-containing silane coupling agents (Japanese Patent Application Publication Nos. 9-295988, 9-296135, and 9-295989), monomethylamino group-containing silane coupling agents (commercial products), benzimidazole group-containing silane coupling agents (Japanese Patent Application Publication No. 6-279458), benzotriazole group-containing silane coupling agents (Japanese Patent Application Publication No. 6-279463), or pyridine ring-containing silane coupling agents (Japanese Patent Application Publication Nos. 9-295990 and 9-295991).